The present invention is directed to air bearing support apparatus for drying a moving web and more particularly an apparatus which includes radiant heaters located in the cross-direction of the moving web which may be individually controlled to provide an even moisture profile.
As, disclosed in a co-pending application, Ser. No. 475,125, filed Mar. 14, 1983, in the name of ERIK STEPHANSEN ET AL, and entitled APPARATUS FOR DRYING A MOVING WEB, and now U.S. Pat. No. 4,494,316, in the paper making industry where there is a continuously moving sheet of paper being produced, there is a need for providing a drying technique which eliminates moisture streaks in the moving or machine direction of the web to therefore provide a smooth cross-direction moisture profile. The above co-pending application discloses and claims details of a dryer unit which are utilized in the present invention. Thus, the above co-pending application is incorporated herewith by reference.
One problem that is inherent in any paper making process with a moving web is the inevitable flutter or movement of the paper in the direction perpendicular to the direction of movement of paper itself normally termed the "machine direction". One solution to this problem is installing heater apparatus as disclosed in the above co-pending STEPHANSEN patent application at a point of the paper making process where the paper is more stable; for example, as it is entering or is on, for example, a calender roll. Or, alternatively, when the paper is entering or being rolled over the cylindrical steam drums which are also used for the drying of the paper web. But, of course, this technique can normally only be used where the dryer occupies only one surface of the paper.
Where it is desired to utilize a dryer technique where the apparatus is juxtaposed on opposite sides of the moving sheet or web with the units facing one another then the problem of paper movement may be significant. One solution suggested is by a Smith, Jr. U.S. Pat. No. 3,793,741 which illustrates heating units on opposite sides of a moving web and shows inclined nozzles which while used for drying also are set to minimize the flutter of the web. However, this is mentioned only as incidental effect to the desired "scouring" action of the air from the nozzles. In addition, the Smith, Jr. patent appears to be directed more toward materials other than simple paper which require the removal of "volatiles" which implies thicker materials such as fiberboard, etc., where the flutter problem is less.
One final comment on the flutter problem and that is to avoid breakage or tearing the heater apparatus when it is, for example, in an elongated structural member which lies across the paper, should not contact the moving material.
One simple way of achieving this is spacing it far enough away; but this, of course, decreases drying efficiency.
Thus, it is an object of the present invention to provide an air bearing support apparatus for drying a moving web.
It is another object of the present invention to improve the radiant heating coupling efficiency to the moving web.
In accordance with the above objects, the air bearing support apparatus comprises a first elongated structural member having a length at least as great as the web in a transverse cross-direction and carrying a plurality of side-by-side heater modules for drying the web. It includes an air plenum connected to all of the heater modules. Forced air means supply air to the plenum. Each dryer module includes a plurality of heater elements in close proximity to the web and a solid barrier carried by the dryer module between the heater elements and the web. The barrier is substantially transparent to the heat producing radiation of the heater elements. The barrier includes at least one narrow slit parallel to the line of movement of the web for allowing the passage of air from the air plenum to the space between the web and barrier.
Juxtaposed on the opposite side of the web is a second elongated structural member, the two structural members providing a gap in which the web may be inserted for movement. The solid barrier of the second member includes narrow slits, also parallel to the line of movement of the web.
The second member includes an air plenum connected to all of the slits of its solid barrier for allowing the passage of air from the air plenum to the space between the web and the barrier. Thus, an air bearing is provided for the moving web inserted in the gap. Forced air means also supply air to the air plenum of the second elongated structural member.